Polyesters based on terephthalic acid, ethylene glycol and 1,4-cyclohexanedimethanol are useful for producing clear articles by injection molding or extrusion. For many applications, these materials have sufficient thermal dimensional stability. However, for other applications such as medical devices requiring steam sterilization, there is a need for further improvements in thermal dimensional stability. Some improvements have occurred in this area. For example, polyesters have been blended with polystyrene as disclosed in U.S. Pat. No. 3,644,574, assigned to Eastman Kodak Company, Rochester, N.Y. Polyesters have also been blended with styrene maleic anhydride copolymers as disclosed in U.S. Pat. No. 4,891,405, assigned to Arco Chemical Co. Also, polyesters have been blended with acrylonitrilebutadiene styrene-polymers as disclosed in Modern Plastics Encyclopedia published in 1990 by McGraw Hill, Inc. However, blends containing significant quantities of dissimilar polymers are typically opaque.
Surprisingly, we have found that blends of certain polyesters with polyphenylene oxide (or polyphenylene ether) polymers exhibit marked clarity. Polyphenylene ether polymers are clear and possess attractive thermal dimensional stabilities, but they are difficult to process and relatively expensive. These deficiencies can be overcome by adding other polymers, such as high impact polystyrene as disclosed in British Patent 1,125,628 by R. W. Finholt, assigned to General Electric Company, or polycarbonate as disclosed in U.S. Pat. No. 4,401,649, assigned to Borg Warner Chemicals. These compositions are generally opaque.
Therefore, there is a continuing need in various research and industrial arts for polyesters having good thermal dimensional stability, clarity, ease in processing, and economic feasibility.